Membrane electrochemical generator

ABSTRACT

A membrane electrochemical generator comprises a multiplicity of reaction cells ( 101 ) mutually connected in series and assembled according to a filter-press type configuration. Each reaction cell is delimited by a pair of conductive bipolar plates ( 103 ), which comprises a multiplicity of first calibrated holes ( 113   a ) for the passage of the gaseous reactants and a multiplicity of second calibrated holes ( 113   b ) for the discharge of the reaction products and of the optional residual reactants. The cooling cells ( 102 ) comprises a rigid peripheral portion ( 102   a ), whereupon a gasket ( 117 ) is laid, defining and sealing on each face of such peripheral portion a zone of collection of the gaseous reactants ( 118   a ) and a zone of collection of the reaction products and of the residual reactants ( 118   b ). In a filter-press configuration, these two zones are respectively overlaid to the first calibrated holes to reach the active area of the reaction cells ( 101 ).

This application is a 371 of PCT/EP03/04207 filed Apr. 23, 2003.

DESCRIPTION OF THE INVENTION

The present invention relates to a membrane electrochemical generatorhaving reduced size.

Processes of energy conversion of chemical energy to electric energybased on membrane electrochemical generators are known in the art.

An example of membrane electrochemical generator is shown schematicallyin FIG. 1. The electrochemical generator 1 is formed by a multiplicityof reaction cells 2 mutually connected in series and assembled accordingto a filter-press configuration.

Each reaction cell 2 converts the free energy of reaction of a firstgaseous reactant (fuel) with a second gaseous reactant (oxidant) withoutdegrading it completely to the state of thermal energy, thereby withoutbeing subject to the limitations of Carnot's cycle. The fuel is suppliedto the anodic chamber of the reaction cell 2 and consists for instanceof a mixture containing hydrogen or light alcohols, such as methanol orethanol, while the oxidant is supplied to the cathodic chamber of thesame cell and consists for instance of air or oxygen. The fuel isoxidised in the anodic chamber simultaneously releasing H⁺ ions, whilethe oxidant is reduced in the cathodic chamber, consuming H⁺ ions. Anion-exchange membrane separating the anodic chamber and the cathodicchamber allows the continuous flux of H⁺ ions from the anodic chamber tothe cathodic chamber while hindering the passage of electrons. In thisway, the difference of electric potential established at the poles ofthe reaction cell 2 is maximised.

More in detail, each reaction cell 2 is delimited by a pair ofconductive bipolar plates 3, having planar faces, among which arecomprised, proceeding outwards, the ion-exchange membrane 4; a pair ofporous electrodes 5; a pair of catalytic layers 6 deposited at theinterface between the membrane 4 and each of the porous electrodes 5; apair of current collectors/distributors 7 electrically connecting theconductive bipolar plates 3 to the porous electrodes 5 whiledistributing the gaseous reactants; a pair of sealing gaskets 8 directedto seal the periphery of the reaction cell 2 in order to avoid theescape of gaseous reactants.

In the conductive bipolar plates 3 and in the sealing gaskets 8 of eachreaction cell 2, first openings are present, not shown in FIG. 1, whichare connected to the anodic chamber and the cathodic chamber of the cellitself through distribution channels, also not shown in FIG. 1. Thedistribution channels are obtained in the thickness of the sealinggaskets 8 and have a comb-like structure. They distribute and collect ina uniform fashion within each reaction cell 2 the gaseous reactants andthe reaction products, the latter being mixed with the optional residualreactants.

The sealing gaskets 8 are also provided with second openings for thepassage of a cooling fluid (typically deionised water).

The coupling between the above mentioned openings determines theformation of two upper longitudinal ducts 9, of two lower longitudinalducts 10 and of lateral ducts, not shown in FIG. 1. The two upperlongitudinal ducts 9, only one of which is shown in FIG. 1, definefeeding manifolds for the gaseous reactants (fuel and oxidant), the twolower longitudinal ducts 10, only one of which is shown in FIG. 1,define discharge manifolds for the reaction products (water) mixed withthe optional residual reactants (gaseous inerts and unconverted fractionof reactants) whilst the lateral ducts define feeding manifolds for thecooling fluid. As an alternative, the lower longitudinal ducts 10 may beused as feeding manifolds, and the upper longitudinal ducts 9 asdischarge manifolds. It is also possible to feed one of the two gaseousreactants through one of the upper longitudinal ducts 9, using thecorresponding lower longitudinal duct 10 for the discharge, whilefeeding the other gaseous reactant through the other lower longitudinalduct 10 using the corresponding upper longitudinal duct 9 for thedischarge.

Externally to the assembly of reaction cells 2, two conductive terminalplates 11 are present, delimiting the electrochemical generator 1. Oneof the two conductive terminal plates 11 is provided with nozzles, notshown in FIG. 1, for the hydraulic connection of the upper and lowerlongitudinal ducts 9 and 10 and of the lateral ducts. Moreover, both ofthe conductive terminal plates 11 are provided with suitable holes (alsonot shown in FIG. 1) for housing tie-rods, by means of which thetightening of the electrochemical generator 1 is achieved.

The known electrochemical generator 1 may also comprise a multiplicityof cooling cells (not shown in FIG. 1), interposed between the reactioncells 2 in a 1:1, 1:2 or 1:3 ratio with respect to the same reactioncells. The cooling cells are entirely similar to the reaction cells 2except that they do not comprise the electrochemical package composed bythe ion-exchange membrane 4, the porous electrodes 5 and the catalyticlayers 6 on the inside thereof.

The known electrochemical generator 1, although advantageous underseveral aspects, presents however the drawback of being not achievablewith an overall size below a limit value determined by the thickness ofthe sealing gaskets 8. In fact, the thickness of the sealing gasket 8must allow the obtainment of the distributing channels.

Membrane electrochemical generators are also known wherein the gaseousreactants are distributed through channels directly obtained on thefaces of the conductive bipolar plates. In this case, the distributingchannels connect the upper longitudinal ducts to the lower longitudinalducts acting as paths for the passage of gases and covering the majorityof the electrode surface. Also these electrochemical generators presentan excessive thickness of the reaction cell due to the technicaldifficulty of realising the distributing channels using thin plates.

The object of the present invention is to provide a membraneelectrochemical generator, free from the described drawbacks.

According to the present invention, a membrane electrochemical generatoris provided as defined in claim 1.

For a better understanding of the invention, an embodiment thereof ishereby described, as a mere non limiting example and making reference tothe attached drawings, wherein:

FIG. 1 shows an exploded side-view of a membrane electrochemicalgenerator realised according to the prior art;

FIG. 2 shows a cross-section of a portion of a membrane electrochemicalgenerator realised according to the invention;

FIGS. 3 a and 3 b show front-views of components of the electrochemicalgenerator of FIG. 2;

FIGS. 4 a, 4 b show front-views of further components of theelectrochemical generator of FIG. 2; and

FIG. 5 shows the path of the gaseous reactants within theelectrochemical generator of FIG. 2.

FIG. 2 shows a cross-section of a portion of a membrane electrochemicalgenerator 100 formed by a multiplicity of reaction cells 101 and ofcooling cells 102 mutually connected in series and assembled accordingto a filter-press type configuration, each cooling cell 102 beinginterposed between a pair of reaction cells 101.

More in detail, each reaction cell 101 is delimited by a pair ofconductive bipolar plates 103 with planar faces between which arecomprised, proceeding outwards, an ion-exchange membrane 104; a pair ofporous electrodes 105; a pair of current collectors/distributors 106electrically connecting the conductive bipolar plates 103 to the porouselectrodes 105; a pair of sealing gaskets 107 directed to seal theperiphery of the reaction cell 101 with the purpose of avoiding theescape of the gaseous reactants.

The conductive bipolar sheets 103, shown in FIGS. 3 a, 3 b, have asubstantially rectangular shape and a typical thickness of 0.1-0.4 mm.They present a peripheral portion 108 provided with first and secondupper openings 108 a ₁, 108 a ₂, first and second lower openings 108 b₁, 108 b ₂ and side openings 109. The peripheral portion 108 is alsoprovided with a multiplicity of openings 110 for housing the tie-rods bymeans of which the tightening of the electrochemical generator 100 isachieved.

As shown in FIG. 3 b, the sealing gaskets 107 are laid on one face onlyof each conductive bipolar plate 103 by moulding (injection orcompression), mechanical anchoring or sticking. They provide the seatfor the current collectors/distributors 106 besides delimiting thereaction cell 101 active area.

In particular, the sealing gaskets 107 are made of a soft material, forexample silicone, elastomer, etc., and present a final thickness thatmay vary between some tenth of a millimeter to a few millimeters.

Each conductive bipolar plate 103 is also provided with a multiplicityof upper calibrated holes 113 a and a multiplicity of lower calibratedholes 113 b with a diameter comprised between 0.1 mm and 5 mm. Throughthe multiplicity of upper calibrated holes 113 a, the gaseous reactantsproceeding from the adjacent cooling cell 102 flow, while through themultiplicity of lower calibrated holes 113 b the reaction products andthe residual reactants leave the reaction cell 101, as will be explainedbelow in more detail. The upper calibrated holes 113 a are mutuallyaligned with the purpose of ensuring a homogeneous distribution of thegaseous reactants and are placed below the first and second upperopenings 108 a ₁, 108 a ₂. The lower calibrated holes 113 b are in theirturn mutually aligned and are placed above the first and second loweropenings 108 b ₁, 108 b ₂. Both the upper 113 a and the lower calibratedholes 113 b are positioned at a distance of about 1 mm from the sealinggasket 107, in order to better exploit the reaction cell 101 activearea.

During the assemblage of the electrochemical generator 100, the couplingbetween the first and second upper openings 108 a ₁, 108 a ₂ of all theconductive bipolar plates 103 determines the formation of two upperlongitudinal ducts 111 while the coupling between the first and secondlower openings 108 b ₁, 108 b ₂ of all the conductive bipolar plates 103determines the formation of two lower longitudinal ducts 112. The twoupper longitudinal ducts 111, only one of which is shown in FIG. 2,define the feeding manifolds of the gaseous reactants (fuel and oxidant)while the two lower longitudinal ducts 112, only one of which is shownin FIG. 2, define the discharge manifolds of the reaction products mixedwith the optional residual reactants. As an alternative, the lowerlongitudinal ducts 112 may be used as the feeding manifolds, and theupper longitudinal ducts 111 as the discharge manifolds. It is alsopossible to feed one of the two gaseous reactants through one of the twoupper longitudinal ducts 111, using the corresponding lower longitudinalduct 112 for discharging, while feeding the other gaseous reactantthrough the other lower longitudinal duct 112 using the correspondingupper longitudinal duct 111 for discharging.

Furthermore, the coupling between the side openings 109 of all theconductive bipolar sheets 103 determines the formation of lateral ductsnot shown in FIG. 2 for the passage of a cooling fluid.

Making now reference to FIGS. 4 a, 4 b, each cooling cell 102 has asubstantially rectangular shape and dimensions equivalent to those ofthe reaction cell 101. Each cooling cell 102 comprises a rigidperipheral portion 102 a, made of plastics or metal, acting as theseparating surface for the two gaseous reactants, and a hollow centralportion 102 b to provide the seat of the current collector/distributor106 through which the heat exchange takes place. The rigid peripheralportion 102 a is provided with first and second upper openings 114 a ₁,114 a ₂, first and second lower openings 114 b ₁, 114 b ₂ and sideopenings 115. In the filter-press configuration, the first and secondupper openings 114 a ₁, 114 a ₂ of the cooling cells 102 form, inconjunction with the first and second upper openings 108 a ₁, 108 a ₂ ofthe reaction cells 101 the two upper longitudinal ducts 111 while thefirst and second lower openings 114 b ₁, 114 b ₂ of the cooling cells102 form, in conjunction with the first and second lower openings 108 b₁, 108 b ₂ of the reaction cells 101, the two lower longitudinal ducts112. The side openings 115 of the cooling cells 102 form in their turn,in conjunction with the side openings 109 of the reaction cells 101, thefeeding manifolds of the cooling fluid. The rigid peripheral portion 102a is also provided with a multiplicity of holes 116 for housing thetie-rods by means of which the tightening of the electrochemicalgenerator 100 is achieved.

Moreover, each cooling cell 102 comprises gaskets 117 which are laid oilboth faces of the rigid peripheral portion 102 a so as to define on eachface of such peripheral portion a zone of collection of the gaseousreactants 118 a positioned below the first and second upper openings 114a ₁, 114 a ₂; a zone of collection of the reaction products and of theresidual reactants 118 b positioned above the first and second loweropenings 114 b ₁, 114 b ₂; a feeding channel 119 to connect one of thetwo upper openings 114 a ₁, 114 a ₂ to the zone of collection of thegaseous reactants 118 a; a discharge channel 120 to connect the zone ofcollection of the reaction products and of the residual reactants 118 bto one of the lower openings 114 b ₁, 114 b ₂; side channels 121 for theinlet and the outlet of the cooling fluid placed in correspondence ofthe zone of collection of the gaseous reactants 118 a and of the zone ofcollection of the reaction products and of the residual reactants 118 b.In the filter-press configuration, the zone of collection of the gaseousreactants 118 a is overlaid to the upper calibrated holes 113 a whilethe zone of collection of the reaction products and of the residualreactants is overlaid to the lower calibrated holes 113 b. The gaskets117 seal the zone of collection of the gaseous reactants 118 a and thezone of collection of the reaction products and of the residualreactants 118 b so as to hinder the passage of the gaseous reactants, ofthe reaction products and of the residual reactants within the coolingcell 102.

Furthermore, the gaskets 117 are made of a soft material (silicone,elastomer, etc.) compatible with the tightening/assemblage loads imposedby the sealing gaskets 107 of the reaction cell 101, and are laid on therigid peripheral portion 102 a through moulding (injection orcompression), mechanical anchoring or sticking.

The electrochemical generator 100 operates as follows. The gaseousreactants (fuel and oxidant) which are supplied to the electrochemicalgenerator 100 through the upper longitudinal ducts 111 flow to the zoneof collection of the gaseous reactants 118 a through the feedingchannels 119. The gaseous reactants, being prevented from flowing withinthe cooling cells 102, pass herefrom through the multiplicity of uppercalibrated holes 113 a placed on the conductive bipolar plates 103 ofthe adjacent reaction cells 101 (FIG. 5). In this way the gaseousreactants reach the reaction cell 101 active area where the properreaction takes place.

The reaction products and the residual reactants produced in thereaction cells 101 pass in their turn through the multiplicity of lowercalibrated holes 113 b positioned on the conductive bipolar plates 103of the same reaction cells (FIG. 5), reaching the zones of collection ofthe discharge products 118 b of the adjacent cooling cells 102.Herefrom, they leave the electrochemical generator 100 through thedischarge channels 120.

The cooling fluid supplied through the side ducts enters and leaves thecooling cells 102 through the side channels 121 while the distributionthereof inside such cells is deputed to the currentcollectors/distributors 106.

Thus, according to the present invention, the cooling cells 102 performthe dual function of chambers for the passage of the cooling fluid andof chambers for the passage of the gaseous reactants, of the reactionproducts and of the residual reactants.

The advantages that can be achieved with the membrane electrochemicalgenerator 100 are the following.

Firstly, the membrane electrochemical generator 100 presents aremarkably reduced overall size with respect to the knownelectrochemical generators. In fact, the replacement of the distributingchannels obtained within the thickness of the sealing gaskets with theupper and lower calibrated holes 113 a, 113 b realised on the conductivebipolar plates 103 allows employing components of minimal thickness,particularly as regards the gaskets.

Moreover, the replacement of the distributing channels with thecalibrated holes allows an improved sealing of gaskets 107 and ofgaskets 117, which now result completely flat. It is finally apparentthat modifications and changes may be made to the disclosedelectrochemical generator 100, without departing from the extent of thepresent invention.

1. A membrane electrochemical generator fed with gaseous reactants andcomprising a multiplicity of reaction cells (101) mutually connected inseries and assembled according to a filter-press type configuration,each reaction cell (101) being delimited by a pair of conductive bipolarplates (103) with flat faces between which are comprised, proceedingoutwards, an ion-exchange membrane (104); a pair of porous electrodes(105); a pair of current collectors/distributors (106) electricallyconnecting said conductive bipolar plates (103) to said porouselectrodes (105), said bipolar plates (103) having upper openings (108 a₁, 108 a ₂) and lower openings (108 b ₁, 108 b ₂) obtained on aperipheral portion (108) thereof, said upper and lower openings (108 a₁, 108 a ₂; 108 b ₁, 108 b ₂) determining the formation of upper andlower longitudinal ducts (111; 112) which define feeding manifolds forgaseous reactants and discharge manifolds for reaction products andoptional residual reactants, respectively, wherein the said conductivebipolar plates (103) comprise a multiplicity of mutually aligned uppercalibrated holes (113 a) arranged below said upper openings (108 a ₁,108 a ₂) and a multiplicity of mutually aligned lower calibrated holes(113 b) arranged above said lower openings (108 b ₁, 108 b ₂) for thepassage of said gaseous reactants from an adjacent cell and for thedischarge of the reaction products and of the optional residualreactants, respectively.
 2. A generator of claim 1, wherein said uppercalibrated holes (113 a) and said lower calibrated holes (113 b) areplaced at a distance of about 1 mm from a sealing gasket (107) coveringonly one face of said peripheral portion (108), said sealing gasket(107) providing a seat for the current collector (106) and delimitingthe active area of the reaction cell (101).
 3. A generator of claim 2,wherein said sealing gasket (107) is laid on said peripheral portion(108) by injection molding or compression molding or mechanicalanchoring or sticking.
 4. A generator of claim 2, wherein said sealinggasket is made of a soft material comprising silicone or elastomers andsaid sealing gasket (107) presents a thickness that may vary betweensome tenths of a millimeter to a few millimeters.
 5. A generator ofclaim 1 wherein said upper calibrated holes (113 a) and said lowercalibrated holes (113 b) have a diameter between 0.1 mm and 5 mm.
 6. Agenerator of claim 1 further comprising a plurality of cooling cells(102), each cooling cell (102) being interposed between a pair ofreaction cells (101).
 7. A generator of claim 6, wherein each coolingcell (102) comprises a rigid peripheral portion (102 a) and a hollowcentral portion (102 b), said rigid peripheral portion (102 a) acting asa separating surface for said gaseous reactants and said hollow centralportion (102 b) providing the seat of a corresponding currentcollector/distributor (106).
 8. A generator of claim 7, wherein saidrigid peripheral portion (102 a) is provided with feeding openings (114a ₁, 114 a ₂) and discharge openings (114 b ₁, 114 b ₂), said feedingopenings (114 a ₁, 114 a ₂) of said rigid peripheral portion (102 a) ofsaid cooling cells (102) forming feeding longitudinal ducts (111) inconjunction with said feeding openings (108 a ₁, 108 a ₂) of saidperipheral portion (108) of said conductive bipolar plates (103) andsaid discharge openings (114 b ₁), 114 b ₂) of said rigid peripheralportion (102 a) of said cooling cells (102) forming longitudinaldischarge ducts (112) in conjunction with said discharge openings (108 b₁, 108 b ₂) of said peripheral portion (108) of said conductive bipolarplates (103).
 9. A generator of claim 8 wherein said rigid peripheralportion (102 a) is covered on each face by a gasket (117), said gasket(117) defining on each face of said rigid peripheral portion (102 a) azone of collection of the gaseous reactants (118 a) placed incorrespondence of said feeding openings (114 a ₁, 114 a ₂) of said rigidperipheral portion (102 a), a zone of collection of the reactionproducts and of the residual reactants (118 b) placed in correspondenceof said discharge openings (114 b ₁), 114 b ₂) of said rigid peripheralportion (102 a), a feeding channel (119) to connect one of said feedingopenings (114 a ₁, 114 a ₂) to said zone of collection of the gaseousreactants (118 a), a discharge channel (120) to connect said zone ofcollection of the reaction products and of the residual reactants (118b) to one of said discharge openings (114 b ₁, 114 b ₂).
 10. A generatorof claim 9, wherein said gaskets (117) seal said zone of collection ofthe gaseous reactants (118 a) and said zone of collection of thereaction products and of the residual reactants (118 b) so as to hinderthe passage of said gaseous reactants and of said reaction products andoptional residual reactants within said cooling cell (102).
 11. Agenerator of claim 9 wherein, in a filter-press configuration, said zoneof collection of the gaseous reactants (118 a) is overlaid to said firstcalibrated holes (113 a) and said zone of collection of the reactionproducts and of the residual reactants (118 b) is overlaid to saidsecond calibrated holes (113 b).
 12. A generator of claim 9 wherein saidgasket (117) is laid on said rigid peripheral portion (102 a) by meansof injection molding or compression molding or mechanical anchoring orsticking and that said gasket (117) is made of a soft materialcomprising silicones, elastomers, etc.
 13. A generator of claim 9,wherein said rigid peripheral portion (102 a) of said cooling cells(102) is provided with side openings (115) for the passage of a coolingfluid and of inlet and outlet side channels (121) of said cooling fluid,said side channels (121) being placed respectively in correspondence ofsaid zone of collection of the gaseous reactants (118 a) and of saidzone of collection of the reaction products and of the residualreactants (118 b).
 14. A generator of claim 7 wherein said rigidperipheral portion (102 a) is made of plastics or metal.